Filters that filter out the damaging spectral portions of the light are usually used in surgical microscopes.
DE-A1-33 39 172 describes a light trap for surgical microscopes. Zones of the illuminated field in the object field are shadowed using a stop that can be pivoted into the illumination beam path of a surgical microscope. The shadowing of the center of the illuminated field in the region of the pupil prevents a damaging light beam from striking the retina of the patient's eye. A dark spot is therefore formed at the center of the illuminated field above the patient's pupil.
The disadvantage here, however, is that this absorption of light by the stop in the center of the illumination beam path results in waste heat, so that, for example, the support material might crack. In addition, a not inconsiderable portion of the light is lost as a result of the light-absorbing coating of the stop.